Vehicles utilized to support heavy loads, such as trucks, usually include a frame of welded or riveted components which purposely allow the frame to twist slightly under lateral deformation in order to permit the vehicle to accommodate itself to irregularities in the road surface and maintain adequate road contact.
However, when a vehicle is utilized to support aerial equipment such as extendable ladders as used on fire trucks, such apparatus imparts very high bending and lateral twisting forces upon the vehicle frame which are unacceptable for safe aerial ladder use. Accordingly, it is the common practice with aerial fire fighting vehicles to fabricate a "torque box" having great resistance to twisting and support such torque box upon a conventional truck framework chassis and mount the aerial apparatus on the torque box. The torque box may have hydraulically actuated ground-engaging jacks on outriggers mounted thereon, and the rigid nature of the torque box permits the extended aerial equipment to be safely used.
The fabrication of a separate torque box within a conventional vehicle frame is expensive, and special connecting apparatus must be interposed between the conventional vehicle frame and the torque box portion. Furthermore, in view of the high strength characteristics of the lightweight vehicle frame it is usually necessary to form this frame of an expensive alloy steel having 110,000 pound tensile strength, and such high strength steel is not readily welded, but rather, bolts and fasteners are required for assembly.
It is an object of the invention to provide a torque box frame for a vehicle capable of supporting aerial apparatus wherein the frame, itself, constitutes a torque box capable of resisting lateral twisting forces imposed thereon by extended aerial apparatus.
Yet another object of the invention is to provide a torque box vehicle frame which has great resistance to lateral twisting, but may be fabricated from readily available components by conventional welding techniques.
A further object of the invention is to provide a vehicle torque box frame which has sufficient rigidity to permit the use of low strength tensile resistance steel, and yet adequately provide a stable support for aerial devices.
In the practice of the invention the vehicle frame is of an elongated form and is of a box configuration in transverse cross section. The lateral sides of the frame are formed of channel beams wherein the legs thereof extend toward each other. The upper plate of the frame is affixed to the upper channel legs, and the lower plate is welded or otherwise attached to the lower legs.
The lower portion of the frame is of a generally concave form to provide clearance for the vehicle driveshaft, and a water conduit may extend through the frame within the box configuration for the purpose of supplying water to fire fighting apparatus located on the aerial equipment.
Internally, K-bracing extends between the frame lateral sides in the form of plates having a vertical dimension substantially equal to the frame box vertical dimension. The K-bracing plates are welded to the lateral sides, and the lower edge thereof is of a form including a concave configuration to accommodate itself to the concave form of the bottom frame plate. The K-bracing reinforcing plates are welded to the bottom plate, as well as the lateral sides, and the presence of the K-bracing further greatly adds to the rigidity of the frame.